Structure based drug discovery of potent and specific antimicrobial agents for anthrax

Infections by pathogenenic microbes are an increasing problem due to a lack of universal vaccines and growing resistance to current antibiotics. The constant battle for researchers in the fight against pathogens is to design new and improved drugs capable of curing an infection. In this thesis I take a well validated drug target, Dihydrofolate reductase (DHFR), which is essential for cell viability and pursue a multi-vectored approach to design effective new inhibitors against the bacteria Bacillus cereus which is closely genetically related to Bacillus anthracis. Bacillus is naturally resistant to the known bacterial antifolate, trimethoprim (TMP), due to lack of affinity between the enzyme and inhibitor. Despite this apparent resistance to TMP, other classes of DHFR inhibitors may bind the enzyme with sufficient potency to suggest further development.; To explore the potential of DHFR as a drug target against Bacillus, 27 compounds were screened against the enzyme from B. cereus which is 98% identical to the enzyme from B. anthracis. Several 2,4-diamino-5-deazapteridine compounds displayed sub micromolar IC50 values that translated well to in vivo toxicity against B. cereus, the most potent compounds with MIC 50 and MBC50 values of 1.6 mug/mL and 0.09 mug/mL, respectively. A structure-activity relationship (SAR) for the inhibitors was built based on homology models of the B. anthracis and B. cereus DHFR proteins. This SAR provided insight into the structure-based design of potent and specific inhibitors against Bacillus.; Next, a newly developed scaffold based on TMP and molecular modeling was used to design inhibitors specific to Bacillus. The best inhibitors exhibit sub-micromolar IC50 values and up to 276-fold specificity. A collaborative effort led to the development of potent inhibitors against Cryptosporidium hominis DHFR using the same scaffold. This scaffold also served in the development of inhibitors against Toxoplasma gondii DHFR and may be useful against additional pathogens. Data presented in this dissertation led to further redesign of these drug leads. These compounds will need to be synthesized and tested to determine if they are viable drug leads.